Diapause-associated transcription of BmEts, a gene encoding an ETS transcription factor homolog in Bombyx mori

To understand the molecular mechanism of diapause determination in early embryogenesis of the silkworm, Bombyx mori, mRNA from diapause and non-diapause eggs was compared using the differential display technique. A 1.2 kbp differentially amplified cDNA fragment was cloned and sequenced. Northern blot analysis confirmed that the mRNA corresponding to this clone, D1, was specifically induced in diapause eggs from 20 h after oviposition, and decreased gradually but was clearly detectable until 40 days after oviposition. On the other hand, if diapause eggs were activated by HCl treatment 20 h after oviposition, the mRNA corresponding to D1 vanished 72 h after HCl treatment. In pnd (pigmented and non-diapausing egg) homozygous embryos, which never enter into diapause, the RNA was not transcribed at any stage, whereas, in pnd-2 homozygous embryos which also have no diapause, similar results were obtained to those for HCl treated eggs. The deduced amino acid sequence of D1 was most highly related to the identified Drosophila and vertebrate ETS proteins, within the ~ 85 amino acid ETS domain. ETS proteins play an important role in transcription activation during a variety of biological processes and can be grouped into sub-families, based on sequence similarity in the ETS domain which has been shown to be a DNA-binding domain. Therefore, we have called the gene corresponding to D1 BmEts. These observations suggest that BmEts encodes a novel ETS family member which is strongly associated with the embryonic diapause. Moreover, BmEts probably acts downstream of the pnd gene in the regulatory hierarchy of diapause determination, alternatively BmEts itself might be the pnd gene.